1. Field of the Invention
The invention is in the field of coating apparatus for use in coating by vaporized material in a vacuum chamber.
2. Description of the Prior Art
In vacuum coating processes, it is sometimes desirable to hold the substrate to be coated at an angle with respect to the source of coating vapor. Further, proper coating of the substrate may require that it be continuously rotated about a particular axis. When the substrate is a turbine engine part which is to be coated with a special alloy which is resistant to corrosion at high temperatures, the coating process involves substrate temperatures exceeding 800 C and pressures of less than 10.sup.-2 Torr. Frequently, the coating process requires 1100 C and 10.sup.-5 Torr. All equipment within the coating chamber must then be able to withstand these extremes of temperature and pressure and must not contain cavities, lubricants, or other sources of vapor which might contaminte the coating. Additionally, the equipment must operate reliably without being affected by the deposition of coating material.
In the prior art, turbine engine parts have been dangled from the end of a rotatable shaft by a conventional U-joint in which one shaft is pinned between a U-shaped fixture at the end of a second shaft. One problem has been that the mechnical limit on the angle between the shafts of a conventional U-type joint is not constant in all rotational positions of the shafts. Thus, if a part is allowed to dangle to the angular limit of the U-type joint, rotation of one shaft about a fixed horizontal axis causes the part to bob up and down as it rotates. Conventional U-type joints have also not been able to withstand the adverse conditions of the coating process. Despite the use of shields, the excessive heat and the deposition of coating material have caused prior art U-type joints to stiffen or freeze after only a few coating cycles, causing defective coating of the turbine part being processed at the time of the failure. Alternately, the joint pin may loosen and fall out allowing the part to fall into the coating source. The present invention is the culmination of a specific attempt to overcome these and other problems in the prior art.